Construction of the Dulles Corridor Metrorail Project in Tysons Corner. (Jahi Chikwendiu/The Washington Pos)

Tysons Corner planners, landowners and developers have grappled for more than two years with how to pay for needed Tysons-wide transportation improvements.

That was when the expected cost was only $1.7 billion.

In January, state transportation officials broke the news to many Tysons stakeholders that the estimated costs for transportation improvements needed by 2030 had risen to $2.1 billion, up 24 percent from the 2009 estimates. The new estimate includes $300 million to widen Route 7 from the Dulles Toll Road to Reston Avenue, $126 million to extend Boone Boulevard from Route 123 to Ashgrove Lane and $94 million to widen Gallows Road from Route 7 to Prosperity Avenue.

In all, the new estimates call for $1.1 billion for road projects, $519 million for a grid of streets, $408 million for transit projects and $77 million for pedestrian access and bicycle improvements.

Even under the previous estimates, provided in 2009, landowners were struggling to agree on how large a share they were willing to pay.

The disagreement is largely because of a split in the group between those who already enjoy development rights under previous zoning guidelines and those who are seeking rights under the new plan for Tysons Corner.

The former group isn’t inclined to pay for improvements their projects do not require — and which their competitors’ might. This includes Macerich Group, which has announced it plans to build an office building and whose senior vice president of property management, Tim Steffan, has said absorbing the additional costs would be difficult. The group also includes Lerner Enterprises, which has already begun an office project. James D. Policaro, managing director of development for Lerner, did not return a request for comment.

But there are others, among them the Georgelas Group, Cityline Partners and Capitol One, that could benefit on an agreement over planned upgrades.

Thomas D. Fleury, Cityline executive vice president, said that with so many potential costs up in the air, it’s very difficult to prepare to seek zoning approval.

“There is a lot of balls in the air, a lot of smart people working on it, we’re all watching it trying to figure out how all this will get financed,” he said. “What do you commit to if it’s not decided by the time your case gets to a hearing?”

Fairfax County staff has floated three funding scenarios in which landowners would pay either 51, 75 or 90 percent of the total cost. Each includes a different assortment of improvements.

For the private sector to contribute to the costs, either a majority of landowners or owners of a majority of the land will likely have to vote to create a new tax district or multiple mini tax districts. They already voted to pay 22 cents per $100 of assessed land value to finance the first phase of the Silver Line.

Fleury said that if companies such as Macerich and Lerner aren’t on board, it’s hard to see a second Tysons-wide tax attracting the required votes. “If you take them out, you’re just not going to get there,” he said.

For that reason the Tysons Partnership, an advocacy group formed by landowners, has yet to make a proposal. “We are analyzing potential recommendations now,” said Jonathan B. Cox, senior vice president for development at housing developer AvalonBay and active member of the partnership.

The county is ready for a response. “Right now we are waiting for Tysons Partnership to present an approach as to how the private sector prefers to fund its share of the transportation infrastructure,” said Barbara Byron, director of the Fairfax County office of community revitalization, in an e-mail.